Lead frame for fabricating surface mount type semiconductor devices with high reliability

ABSTRACT

A lead frame and a semiconductor device fabricated by using the same. The lead frame comprises: first and second band shaped members disposed parallel to each other; a plurality of island portions for mounting semiconductor pellets thereon having first end portions connected to the first band shaped member; coupling strip each provided for one of the island portions whose first end portion connects to a second end portion of each of the island portions and whose second end portion connects to the second band shaped member. The lead frame further comprises at least one electrode portion for each of the island portions and electrically coupled with a corresponding electrode of the semiconductor pellet. The at least one electrode portion is disposed between each of the island portions and the second band shaped member, a first end portion thereof is connected to the second band shaped member, and a second end portion thereof is opposed to the second end portion of each of the island portions.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application is a division of application Ser. No.09/836,174, filed Apr. 18, 2001, now pending, and based on JapanesePatent Application No. 2000-123672 filed Apr. 19, 2000 by YoshiharuKANEDA and Tokuhiro UCHIYAMA. This application claims only subjectmatter disclosed in the parent application and therefore presents no newmatter.

FIELD OF THE INVENTION

[0002] The present invention relates generally to a surface mount typesemiconductor device and a lead frame used for fabricating the same.More particularly, the present invention relates to downsizing a surfacemount type semiconductor device without deteriorating reliabilitythereof and to realizing a lead frame suitable for such downsizing.

BACKGROUND OF THE INVENTION

[0003] Portable type electronic circuit apparatuses such as a videocamera, a notebook type personal computer and the like are being urgedto be small in size and light in weight. Thus, it is strongly desiredthat electronic parts used in these electronic circuit apparatuses suchas semiconductor devices and the like are also downsized and thinned. Inorder to cope with such requirements, electronic parts themselves aredownsized. Alternatively, even if the external size of each of theelectronic parts is the same or slightly larger than before, electronicelements therein are more highly integrated and, thereby, the electronicparts are made substantially small in size and light in weight.

[0004]FIG. 14 is a partial perspective view illustrating a conventionallead frame used for fabricating a semiconductor device. The lead frame105 shown in FIG. 14 is used for fabricating a power semiconductordevice which emits much heat when operated.

[0005] The lead frame 105 shown in FIG. 14 comprises a pair of bandshaped members, that is, first and second band shaped members 101 and102 disposed parallel to each other. The width of the first band shapedmember 101 is smaller than that of the second band shaped member 102. Inthe second band shaped member 102, holes or perforations 102 a fortransferring the lead frame 105 are formed at intervals of apredetermined constant length. The lead frame 105 further comprisesisland portions or heat sinks 103, and leads 104. The heat sinks 103 aredisposed outside the first band shaped member 101, that is, on theopposite side of the second band shaped member 102, with predeterminedspaces therebetween. The leads 104 comprise lead sets each of which hasmutually parallel three leads 104 a, 104 b and 104 c. A large number oflead sets of the leads 104 extend from an edge portion of the secondband shaped member 102 beyond the first band shaped member 101.Therefore, the first band shaped member 101 is coupled with the secondband shaped member 102 via the leads 104. In each lead set of the leads104, the center lead 104 a is coupled, at an edge portion thereof, withan edge portion of the heat sink 103. End portions of other leads ineach lead set are not coupled with the heat sink, but are located nearthe edge portion of the heat sink 103.

[0006] With reference to the drawings, an explanation will be made on amethod of manufacturing a conventional power semiconductor device. FIG.15 is a side cross sectional view of a conventional power semiconductordevice fabricated by using the lead frame 105 shown in FIG. 14, and FIG.16 is a top perspective view of the semiconductor device. For the sakeof easy understanding, FIG. 16 shows a structure of a portion within anencapsulation resin by using perspective representation.

[0007] First, a semiconductor pellet 107 is mounted on the heat sink 103by using a solder 106. Then, electrodes (not shown in the drawing) onthe semiconductor pellet 107 and the leads 104 b and 104 c areelectrically coupled via wires 108 a and 108 b, respectively. The wire108 a through which a main current flows is constituted of a thick wire.The main portion on the heat sink 103 including the semiconductor pellet107 is coated with an encapsulation resin 109. In this case, the backsurface of the heat sink 103 is exposed from the encapsulation resin109. Also, as shown in FIG. 16, the lead 104 a is disposed in a concaveportion 109 a of the encapsulation resin 109. Therefore, the surface ofthe encapsulation resin 109 from which the lead 104 a coupled with theheat sink 103 comes out is recessed from the surface of theencapsulation resin 109 from which other leads 104 b and 104 c come out.Thereby, creepage distances between the lead 104 a and the leads 104 band between the lead 104 a and 104 c can be elongated, and it ispossible to assure a safe operation of the semiconductor device at ahigh voltage.

[0008] After encapsulation by the encapsulation resin 109 is completed,unnecessary portions of the first and second band shaped members 101 and102 of the lead frame 105 which connect the leads 104 are cut andremoved. Thereby, the leads 104 are separated and the semiconductordevice shown in FIG. 16 is completed.

[0009] Also, the center lead 104 a is cut within the concave portion 109a of the encapsulation resin 109. Each of the leads 104 b and 104 c isbent into a crank shape near the encapsulation resin 109. Thereby, endportions of the leads 104 b and 104 c are made coplanar with the exposedsurface of the heat sink 103. FIG. 17 is a side cross sectional viewshowing a conventional surface mount type power semiconductor devicewhich is manufactured in this way. In the semiconductor device shown inFIG. 17, it is possible to directly solder the heat sink 103 and theleads 104 b and 104 c to conductive islands of a wiring substrate notshown in the drawing. Therefore, it is possible to lower the height ofthe semiconductor device mounted on the wiring substrate. Semiconductordevices of this type are disclosed, for example, in Japanese utilitymodel laid-open publication No. 62-188149, Japanese patent laid-openpublication No. 4-340264, Japanese patent laid-open publication No.5-283574 and the like.

[0010] In the above-mentioned conventional semiconductor device, it ispossible to lower the height thereof. However, since the leads 104 b and104 c protrude from the encapsulation resin 109, it is impossible tosufficiently reduce the mounting area of the semiconductor device.

[0011]FIG. 18 is a side cross sectional view illustrating anotherconventional surface mount type power semiconductor device which canobviate the above-mentioned disadvantage. FIG. 19 is a bottom view ofthe semiconductor device of FIG. 18. In FIG. 18 and FIG. 19, likereference numerals are used to designate identical or correspondingparts to those of the conventional semiconductor device of FIG. 17, anddetailed description thereof is omitted here. In the semiconductordevice shown in FIGS. 18 and 19, portions of leads 104 b and 104 c neara heat sink 103 are made coplanar with a surface of the heat sink 103.Also, at the bottom surface of the semiconductor device, portions of theleads 104 b and 104 c together with the heat sink 103 are exposed froman encapsulation resin 109. Leads 104 a, 104 b and 104 c coming out fromthe encapsulation resin 109 are cut in the proximity of theencapsulation resin 109. By using this structure, it is possible tofurther downsize the semiconductor device.

[0012] In the semiconductor device having the structure shown in FIG.18, the area of the heat sink 103 is made as large as possible so thatgood heat dissipating ability can be obtained. However, in thissemiconductor device, it is necessary that the leads 104 b and 104 c aredisposed apart from the lead 104 a. Therefore, the areas of electrodeportions of the leads 104 b and 104 c exposed from the encapsulationresin 109 at the bottom surface of the semiconductor device must berelatively small with respect to the exposed area of the heat sink 103.

[0013] When the semiconductor device having this structure is solderedon conductive land portions of a wiring substrate, the semiconductordevice floats on melted solders and becomes unstable. Therefore, therewas a possibility that the semiconductor device rotates or moves from apredetermined mounting location of the semiconductor device.

[0014] Further, the heat sink 103 and the leads 104 b and 104 c aredisposed coplanar with each other. Therefore, when the thickness of theheat sink 103 is made larger than that of the leads 104 b and 104 c toobtain good heat dissipating ability, the difference of height between asemiconductor pellet 107 and the leads 104 b and 104 c becomes large.

[0015] The outer size of the heat sink 103 is reduced as small aspossible to downsize the semiconductor device. On the other hand, theouter size of the semiconductor pellet 107 is determined from operatingcharacteristics such as an operating current, an operating power and thelike, and reduction of the outer size of the semiconductor pellet 107 islimited. Therefore, the outer sizes of the heat sink 103 and thesemiconductor pellet 107 become close to each other. As a resultthereof, it is impossible to keep an enough distance from an outsideedge portion of the semiconductor pellet 107 to an outside edge portionof the heat sink 103.

[0016] Further, in the power semiconductor device, a main current flowsfrom the heat sink 103 through the semiconductor pellet 107 to a surfaceelectrode of the semiconductor pellet 107, and then reaches the lead 104b via the wire 108 a. The current passed through the semiconductorpellet 107 reaches the wire 108 a via the thin surface electrode of thesemiconductor pellet 107. Therefore, if the wire 108 a is connected to aperipheral portion of the electrode, on-resistance of the semiconductordevice becomes large and an operation at high current is restrained. Inorder to avoid such restraint, as the wire 108 a, a plurality ofseparate wires are used to parallel couple between the electrode of thesemiconductor pellet 107 and the lead 104 b.

[0017] Therefore, it is impossible to couple the surface electrode ofthe semiconductor pellet 107 and the lead 104 b by using the wire 108 avia the shortest distance. There is a possibility that a middle portionof the wire 108 a bends and approaches a peripheral corner portion ofthe semiconductor pellet 107. This deteriorates withstand voltagecharacteristics of the semiconductor device, and at worst causes shortcircuit between the wire 108 a and the semiconductor pellet 107.

[0018] In the conventional lead frame 105, the lead 104 a which supportsthe heat sink 103 at one end thereof has a relatively long portion fromthe heat sink 103 to the first band shaped member 101. Therefore, thelead 104 a bends easily during a manufacturing process of thesemiconductor device. Especially, when the thickness of the heat sink103 is large, there is a possibility that the lead 104 a bends anddeforms at its middle portion due to the weight of the heat sink 103.

[0019] In order to avoid such disadvantage, it may be possible toenlarge the width of the lead 104 a to increase the strength of the lead104 a. When the width of the lead 104 a is enlarged, however, the spacesbetween the lead 104 a and other leads 104 b and 104 c as electrodesbecome short and withstand voltage characteristics of the semiconductordevice are deteriorated. Further, the width of the lead 104 a cannot besufficiently large because of the restriction of the width of theelectrode portion.

[0020] Further, it may be possible to use a conductor tape having arelatively large width in place of the wire 108 a and to realize a lowon-resistance thereby. However, in such case, when the thickness of theencapsulation resin 109 is decreased to thin down the semiconductordevice, it becomes impossible to completely fill the electrode portionwith the resin because the conductor tape becomes a hindrance. Thus,voids are formed in the encapsulation resin 109. Even if such voids donot appear at the outside surface of the encapsulation resin 109, asubstantial thickness of the encapsulation resin 109 becomes small. Thisdeteriorates moisture resistance of the semiconductor device anddeteriorates bonding strength between the electrode portion and theencapsulation resin 109. Therefore, reliability of the semiconductordevice is greatly deteriorated.

SUMMARY OF THE INVENTION

[0021] Therefore, it is an object of the present invention to provide asurface mount type semiconductor device and a lead frame used formanufacturing the same in which the above-mentioned disadvantages of theconventional technology can be obviated.

[0022] It is another object of the present invention to provide asurface mount type semiconductor device and a lead frame used formanufacturing the same in which downsizing of the semiconductor devicecan be attained without deteriorating reliability.

[0023] It is still another object of the present invention to provide asurface mount type semiconductor device which can be mounted preciselyon a predetermined location of a wiring substrate, and a lead frame usedfor manufacturing such semiconductor device.

[0024] It is still another object of the present invention to provide asurface mount type semiconductor device which has an improved withstandvoltage, and a lead frame used for manufacturing such semiconductordevice.

[0025] It is still another object of the present invention to provide asurface mount type semiconductor device which has an improved moistureresistance, and a lead frame used for manufacturing such semiconductordevice.

[0026] According to an aspect of the present invention, there isprovided a lead frame used for manufacturing semiconductor devices, thelead frame comprising: first and second band shaped members disposedparallel to each other; a plurality of island portions for mountingsemiconductor pellets thereon respectively, wherein the plurality ofisland portions are disposed at predetermined intervals between thefirst and second band shaped members, and wherein a first end portion ofeach of the island portions is connected to the first band shapedmember; a coupling strip provided for each of the island portions,wherein the coupling strip is disposed between each of the islandportions and the second band shaped member, wherein a first end portionof the coupling strip is connected to a second end portion of each ofthe island portions, and wherein a second end portion of the couplingstrip is connected to the second band shaped member; and at least oneelectrode portion which is provided for each of the island portions andwhich is to be electrically coupled with a corresponding electrode ofthe semiconductor pellet mounted on each of the island portions, whereinthe at least one electrode portion is disposed between each of theisland portions and the second band shaped member, wherein a first endportion of the at least one electrode portion is connected to the secondband shaped member, and wherein a second end portion of the at least oneelectrode portion is opposed to the second end portion of each of theisland portions but is not connected to the second end portion of eachof the island portions.

[0027] In this case, it is preferable that the width of the couplingstrip is smallest at the first end portion and becomes gradually largertoward the second end portion, and wherein the width of the at least oneelectrode portion is larger than the width of the coupling strip.

[0028] It is also preferable that the at least one electrode portioncomprises two electrode portions corresponding to each of the islandportions, the first end portions of the two electrode portions areconnected to the second band shaped member on both sides of the couplingstrip.

[0029] It is further preferable that the first band shaped member hasperforations for transferring the lead frame.

[0030] It is advantageous that the width of the second band shapedmember is smaller than the width of the first band shaped member.

[0031] According to another aspect of the present invention, there isprovided a lead frame used for manufacturing semiconductor devices, thelead frame comprising: first and second half frame structure portions;and a plurality of bridge members for connecting the first and secondhalf frame structure portions; wherein each of the first and second halfframe structure portions comprises: first and second band shaped membersdisposed parallel to each other; a plurality of island portions formounting semiconductor pellets thereon respectively, wherein theplurality of island portions are disposed at predetermined intervalsbetween the first and second band shaped members, and wherein a firstend portion of each of the island portions is connected to the firstband shaped member; a coupling strip provided for each of the islandportions, wherein the coupling strip is disposed between each of theisland portions and the second band shaped member, wherein a first endportion of the coupling strip is connected to a second end portion ofeach of the island portions, and wherein a second end portion of thecoupling strip is connected to the second band shaped member; and atleast one electrode portion which is provided for each of the islandportions and which is to be electrically coupled with a correspondingelectrode of the semiconductor pellet mounted on each of the islandportions, wherein the at least one electrode portion is disposed betweeneach of the island portions and the second band shaped member, wherein afirst end portion of the at least one electrode portion is connected tothe second band shaped member, and wherein a second end portion of theat least one electrode portion is opposed to the second end portion ofeach of the island portions but is not connected to the second endportion of each of the island portions; and wherein the first and secondhalf frame structure portions are disposed symmetrically such that thesecond band shaped members are located inside, and wherein the bridgemembers are connected to the second band shaped member of the first halfframe structure portion and to the second band shaped member of thesecond half frame structure portion, thereby connecting the second bandshaped members of the first and second half frame structure portionstogether.

[0032] It is preferable that each of the bridge members has aperforation for transferring the lead frame.

[0033] It is also preferable that, in each of the half frame structureportions, there are provided two electrode portions corresponding toeach of the island portions, the first end portions of the two electrodeportions are connected to the second band shaped member on both sides ofthe coupling strip.

[0034] It is further preferable that each of the bridge members islocated between the coupling strip of the first half frame structureportion and the coupling strip of the second half frame structureportion, wherein a portion of the second band shaped member of the firsthalf frame structure portion connecting to each of the bridge membersdoes not overlap a portion of the second band shaped member of the firsthalf frame structure portion connecting to the electrode portion, andwherein a portion of the second band shaped member of the second halfframe structure portion connecting to each of the bridge members doesnot overlap a portion of the second band shaped member of the secondhalf frame structure portion connecting to the electrode portion.

[0035] It is advantageous that each of the perforations is locatedbetween the coupling strip of the first half frame structure portion andthe coupling strip of the second half frame structure portion.

[0036] It is also advantageous that the width of the coupling strip issmallest at the first end portion and becomes gradually larger towardthe second end portion, and wherein the width of the at least oneelectrode portion is larger than the width of the coupling strip.

[0037] It is further advantageous that the width of the second bandshaped member is smaller than the width of the first band shaped member.

[0038] According to still another aspect of the present invention, thereis provided a surface mount type semiconductor device comprising: aconductive island portion; a semiconductor pellet mounted on the topsurface of the conductive island portion, the semiconductor pellethaving at least one electrode formed on the semiconductor pellet; aconductive strip portion, one end of which connects to a portion of afirst end portion of the conductive island portion; at least oneelectrode portion which is electrically coupled with corresponding oneof the at least one electrode of the semiconductor pellet, each of theat least one electrode portion does not connect to the conductive islandportion; and an encapsulation resin which covers and unifies thesemiconductor pellet, the electrode portion, the conductive islandportion and the conductive strip portion; wherein, at the bottom surfaceof the semiconductor device, the bottom surface of the conductive islandportion and a portion of the bottom surface of each of the at least oneelectrode portion are exposed from the encapsulation resin; wherein theportion of the bottom surface of each of the at least one electrodeportion exposed from the encapsulation resin and the bottom surface ofthe conductive island portion are coplanar with each other; wherein, ata side surface of the encapsulation resin, a first end portion of eachof the at least one electrode portion and a second end portion of theconductive strip portion are exposed from the encapsulation resin;wherein the width of each of the at least one electrode portion islarger than the width of the conductive strip portion; and wherein asecond end portion of each of the at least one electrode portion israised from the exposed surface of each of the at least one electrodeand is located inside the encapsulation resin.

[0039] In this case, it is preferable that the conductive island portionfunctions as a heat sink.

[0040] It is also preferable that the at least one electrode portioncomprises a plurality of electrode portions.

[0041] It is further preferable that the at least one electrode portioncomprises two electrode portions.

[0042] It is advantageous that the encapsulation resin has a concaveportion formed in a side surface of the encapsulation resin, a secondend portion of the conductive strip portion protrudes from the concaveportion, and first end portions of the two electrode portions protrudefrom both side of the concave portion in the side surface of theencapsulation resin.

[0043] It is also advantageous that the at least one electrode iselectrically coupled with the at least one electrode on thesemiconductor pellet by wire bonding.

[0044] It is further advantageous that, among the at least one electrodeon the semiconductor pellet, an electrode through which a main currentis to flow is electrically coupled with a corresponding one of the atleast one electrode portion via a conductive tape.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] These and other features, and advantages, of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich like reference numerals designate identical or corresponding partsthroughout the figures, and in which:

[0046]FIG. 1 is a partial perspective view illustrating a major portionof a lead frame according to the first embodiment of the presentinvention;

[0047]FIG. 2 is a schematic cross sectional view showing a condition ofa semiconductor device according to the present invention duringmanufacture thereof by using the lead frame of FIG. 1;

[0048]FIG. 3 is a schematic cross sectional view showing a condition ofthe semiconductor device during manufacture thereof after the conditionof FIG. 2;

[0049]FIG. 4 is a schematic cross sectional view showing a condition ofa semiconductor device during manufacture thereof after the condition ofFIG. 3;

[0050]FIG. 5 is a schematic partial perspective plan view showing thelead frame of FIG. 1 after forming an encapsulation resin;

[0051]FIG. 6 is a bottom view showing a semiconductor device fabricatedby using the lead frame of FIG. 1;

[0052]FIG. 7 is a schematic partial cross sectional view of thesemiconductor device of FIG. 6, shown as a cross sectional view takenalong the line A-A of FIG. 6;

[0053]FIG. 8 is a schematic partial cross sectional view of anothersemiconductor device, shown as a cross sectional view taken along theline A-A of FIG. 6;

[0054]FIG. 9 is a partial plan view schematically showing a lead frameaccording to the second embodiment of the present invention;

[0055]FIG. 10 is a schematic partial perspective plan view showing thelead frame of FIG. 9 after forming an encapsulation resin;

[0056]FIG. 11 is a perspective view showing a semiconductor devicefabricated by using the lead frame of FIG. 9;

[0057]FIG. 12 is a cross sectional view showing a schematic structure ofa semiconductor device according to still another embodiment of thepresent invention;

[0058]FIG. 13 is a perspective view of the semiconductor device of FIG.12 as viewed from the bottom side thereof;

[0059]FIG. 14 is a partial perspective view illustrating a conventionallead frame used for fabricating a semiconductor device;

[0060]FIG. 15 is a side cross sectional view of a conventional powersemiconductor device fabricated by using the lead frame of FIG. 14;

[0061]FIG. 16 is a top perspective view of the semiconductor device ofFIG. 15;

[0062]FIG. 17 is a side cross sectional view showing a conventionalsurface mount type power semiconductor device fabricated by using thelead frame of FIG. 14;

[0063]FIG. 18 is a side cross sectional view illustrating anotherexample of a conventional surface mount type power semiconductor device;and

[0064]FIG. 19 is a bottom view of the semiconductor device of FIG. 18.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0065] With reference to the drawings, an explanation will be made on alead frame according to an embodiment of the present invention, and asurface mount type semiconductor device manufactured by using the leadframe.

[0066]FIG. 1 is a partial perspective view illustrating a major portionof the lead frame according to the first embodiment.

[0067] The lead frame 1 shown in FIG. 1 comprises a first band shapedmember 2 and a second band shaped member 3 disposed parallel to eachother. The width of the second band shaped member 3 is smaller than thewidth of the first band shaped member 2. The first band shaped member 2has perforations 4 for transferring the lead frame 1. The perforations 4are formed at intervals of a predetermined distance.

[0068] The lead frame 1 further comprises island portions or heat sinks5 disposed between the first band shaped member 2 and the second bandshaped member 3. The heat sinks 5 are disposed with predetermined spacestherebetween. One end of each heat sink 5 is coupled with the first bandshaped member 2. A portion of the other end of each heat sink 5 iscoupled with the second band shaped member 3 via a coupling strip 6. Thethickness of the heat sinks 5 is substantially the same as that of thefirst and second band shaped members 2 and 3. The width of the couplingstrip 6 is smallest at a portion where the coupling strip 6 connects tothe heat sink 5, and becomes gradually larger toward the second bandshaped member 3.

[0069] The lead frame 1 further comprises first and second electrodeportions 7 and 8 which connect with the second band shaped member 3 onboth sides of the coupling strip 6 and which extend toward the heat sink5. End portions of the first electrode portion 7 and the secondelectrode portion 8 do not contact or reach the heat sink 5. The widthof each of the first electrode portion 7 and the second electrodeportion 8 is larger than that of the coupling strip 6.

[0070] The lower surfaces of the first and second band shaped members 2and 3, the heat sink 5, the coupling strip 6, and the first and secondelectrode portions 7 and 8 are located coplanar.

[0071] The lead frame 1 according to the present embodiment has astructure obtained by repeating the portion illustrated in FIG. 1.

[0072] Next, with reference to the drawings, an explanation will be madeon a method of manufacturing a semiconductor device by using theabove-mentioned lead frame 1. FIGS. 2-4 are schematic cross sectionalviews showing a method of manufacturing a semiconductor device in orderof process steps.

[0073] First, the lead frame 1 having the above-mentioned structure isprepared. The lead frame 1 is supported and guided at the first bandshaped member 2 and the second band shaped member 3, and applied to amounting process. As shown in FIG. 2, a semiconductor pellet 9 ismounted on each of the heat sinks 5 via adhesive, for example, solder,not shown in the drawing.

[0074] Then the lead frame 1 is applied to a wire bonding process. Asshown in FIG. 3, electrodes not shown in the drawing on each of thesemiconductor pellet 9 are electrically coupled with the first electrodeportion 7 and the second electrode portion 8 via wires 10 and 11,respectively.

[0075] The lead frame 1 is then applied to a resin molding process. Asshown in FIG. 4, each group including the first and second electrodeportions 7 and 8, the semiconductor pellet 9, and the wires 10 and 11 ismolded by an encapsulation resin 12.

[0076]FIG. 5 is a schematic partial perspective plan view showing thelead frame 1 after forming the encapsulation resin 12 in each of theabove-mentioned groups. An area encircled by a chain line in FIG. 5corresponds to an area where the encapsulation resin 12 is formed. Also,in FIG. 5, the structure under the encapsulation resin 12 isperspectively shown. The encapsulation resin 12 has a recessed portionor a concave portion 13 such that a portion of the coupling strip 6 nearthe heat sink 5 is covered by the encapsulation resin 12 and otherportion of the coupling strip 6 is exposed.

[0077] Thereafter, the lead frame 1 is cut at locations shown by dottedlines 14 of FIG. 5. That is, the first band shaped member 2, the secondband shaped member 3, and the coupling strip 6 are cut at the locationsshown by the dotted lines 14. Thereby, the lead frame 1 is separatedinto individual semiconductor devices 30.

[0078]FIG. 6 is a bottom view showing the semiconductor device 30fabricated in this way. In the semiconductor device 30 shown in FIG. 6,the exposed bottom surface of the heat sink 5 and the exposed bottomsurfaces of the first and second electrode portions 7 and 8 are coplanarwith each other. Therefore, the semiconductor device 30 can beappropriately surface mounted on a wiring substrate and the like notshown in the drawing. Also, at the concave portion 13 of theencapsulation resin 12, a remaining portion of the coupling strip 6protrudes from the encapsulation resin 12 and forms a remainingprotrusion 15.

[0079] Generally, when a semiconductor device is to be mounted on awiring substrate, there is a possibility that a heat sink of thesemiconductor device floating on a melted solder rotates on the solder.However, according to the present embodiment, it is possible, at thebottom surface of the semiconductor device 30, to make each area of theexposed portions of the first and second electrode portions 7 and 8relatively large with respect to the area of the exposed portion of theheat sink 5. Therefore, the first and second electrode portions 7 and 8which are located apart from the heat sink 5 operate to suppressrotation of the semiconductor device 30. Thus, it is possible to preventthe semiconductor device 30 from shifting from the location to bemounted. That is, the semiconductor device 30 can be mounted on apredetermined location on the wiring substrate precisely.

[0080] In the above-mentioned embodiment, the width of the couplingstrip 6 can be smallest at the portion where the coupling strip 6connects to the heat sink 5, and the width of the coupling strip 6 at aportion connecting to the second band shaped member 3 can be relativelylarge. Therefore, it is possible to make the portion of the couplingstrip 6 having a small width very short, so that deformation of the leadframe 1 can be avoided. Also, since the encapsulation resin 12 has theconcave portion 13, it is possible to sufficiently separate theremaining protrusion 15 protruding from the encapsulation resin 12 fromthe first and second electrode portions 7 and 8. To this end, it ispossible to make the distances between the remaining protrusion 15 andthe first electrode portion 7 and between the remaining protrusion 15and the second electrode portion 8 sufficiently large, that is, it ispossible to keep the creepage distances therebetween sufficiently large.As a result thereof, it is possible to obtain a large withstand voltageof the semiconductor device.

[0081]FIG. 7 is a schematic partial cross sectional view of thesemiconductor device 30, taken along the line A-A of FIG. 6. Preferably,in the present embodiment, there is provided a stepped portion 16 or 17at least one of the end portion of the heat sink 5 on the side of thefirst and second electrode portions 7 and 8 and the end portions of thefirst and second electrode portions 7 and 8 on the side of the heat sink5. The stepped portion 16 or 17 can be formed when manufacturing thelead frame 1. In general, if the space between the heat sink 5 and thefirst and second electrode portions 7 and 8 is too small, the followingproblem occurs. That is, in a surface mounting process of asemiconductor device, there is a possibility that liquefied soldercauses short circuit between the heat sink 5 and the first electrodeportion 7 and between the heat sink 5 and the second electrode portion8. However, according to the present embodiment, there are provided thestepped portions 16 or 17 at the end potion of the heat sink 5 or theend portions of the first and second electrode portions 7 and 8, asmentioned above. Therefore, it is possible to increase the creepagedistance between the heat sink 5 and the first and second electrodeportions 7 and 8 which are exposed from the encapsulation resin 12 atthe bottom surface of the semiconductor device. Therefore, an withstandvoltage of the semiconductor device can be sufficiently high, and it ispossible to avoid short circuit by solder between the heat sink 5 andthe first and second electrode portions 7 and 8 in a process of surfacemounting the semiconductor device. Further, by providing the steppedportions 16 and/or 17, it is possible to improve adhesion between theheat sink 5 and the encapsulation resin 12 and between the first andsecond electrode portions 7 and 8 and the encapsulation resin 12. Thus,moisture resistance of the semiconductor device can be improved.

[0082] Also, in the present embodiment, the width of the cutting portionof the coupling strip 6 is relatively small. Therefore, when cutting thecoupling strip 6, undesirous excess external force is not applied to theencapsulation resin 12. Thus, it is possible to cut the coupling strip 6without causing a crack in the encapsulation resin 12 adjacent to thecoupling strip 6.

[0083]FIG. 8 is a partial enlarged cross sectional view showing asemiconductor device according to another embodiment of the presentinvention, and corresponds to FIG. 7. In the semiconductor device ofFIG. 8, there is provided a slant surface 18 or 19 at least at one ofthe end portion of the heat sink 5 and the end portions of the first andsecond electrode portions 7 and 8, in place of the stepped portions 16or 17 of FIG. 7. Other structure of the semiconductor device of FIG. 8is the same as that of the semiconductor device of FIG. 7, and detailedexplanation thereof is omitted here. In the semiconductor device havingthe slant surface 18 or 19 as shown in FIG. 8, it is possible to obtainadvantageous effect similar to that obtained by providing the steppedportion 16 or 17 as shown in FIG. 7.

[0084]FIG. 9 is a partial plan view schematically showing a lead frameaccording to the second embodiment of the present invention. The leadframe 40 shown in FIG. 9 has a structure in which half frame structureportions 1 a and 1 b each corresponding to the lead frame 1 shown inFIG. 1 are unified into one frame member. That is, the structure of thelead frame 40 corresponds substantially to a structure in which the halfframe structure portions 1 a and 1 b are symmetrically opposed such thatsecond band shaped members 3 a and 3 b are disposed inside and in whichthe second band shaped members 3 a and 3 b opposing to each other arecoupled together via bridge members 20. Therefore, the lead frame 40comprises: first band shaped members 2 a and 2 b each corresponding tothe first band shaped member 2 of the lead frame 1 of the firstembodiment; second band shaped members 3 a and 3 b each corresponding tothe second band shaped member 3; heat sinks 5 a and 5 b eachcorresponding to the heat sink 5; the coupling strips 6 a and 6 b eachcorresponding to the coupling strip 6; first electrode portions 7 a and7 b each corresponding to the first electrode portion 7; secondelectrode portions 8 a and 8 b each corresponding to the secondelectrode portion 8; and the bridge members 20.

[0085] Differing from the lead frame 1 of the first embodiment, the leadframe 40 does not have perforations formed in the first band shapedmembers 2 a and 2 b. In the lead frame 40, perforations 21 are formed inthe bridge members 20. The shape of each of the perforations 21 is, forexample, a circle. The center of each of the perforations 21 is located,for example, on the line which connects the center lines of the couplingstrips 6 a and 6 b.

[0086] Each of the bridge members 20 couples: a portion of the secondband shaped member 3 a located between the first electrode portions 7 aand the second electrode portion 8 a which oppose via the coupling strip6 a; and a portion of the second band shaped member 3 b located betweenthe first electrode portions 7 b and the second electrode portion 8 bwhich oppose via the coupling strip 6 b. The width of the bridge member20 including the perforation 21 is smaller than the space between thefirst electrode portion 7 a and the second electrode portion 8 a whichoppose via the coupling strip 6 a. Similarly, the width of the bridgemember 20 including the perforation 21 is smaller than the space betweenthe first electrode portion 7 b and the second electrode portion 8 bwhich oppose via the coupling strip 6 b. Therefore, as shown in FIG. 9,one of the side edge portions of the bridge member 20 is located insidefrom the line connecting the side edge of the first electrode portion 7a and the side edge of the second electrode portion 8 b by a distance W.Also, the other one of the side edge portions of the bridge member 20 islocated inside from the line connecting the side edge of the firstelectrode portion 7 b and the side edge of the second electrode portion8 a by the distance W. By this structure, in a cutting process of thelead frame 40 mentioned later, it becomes possible to simultaneously cutand remove the coupling strips 6 a and 6 b and the bridge members 20.

[0087] In the lead frame 40, the width of each of the second band shapedmembers 3 a and 3 b is smaller than the width of each of the first bandshaped members 2 a and 2 b. Thereby, it becomes possible to reduce thetotal width of the lead frame 40. Also, in the cutting process of thelead frame 40 mentioned later, quantity of portions which are cut andscrapped can be reduced.

[0088] Also, the width of the first band shaped member 2 a and the widthof the first band shaped member 2 b are made as small as possible.Thereby, in the cutting process of the lead frame 40 mentioned later, itis possible to easily cut the first and second band shaped members 2 aand 2 b.

[0089] The lead frame 40 according to the second embodiment has astructure obtained by repeating the portion illustrated in FIG. 9,toward upside and downside of FIG. 9.

[0090] Next, an explanation will be made on a method of manufacturing asemiconductor device by using the above-mentioned lead frame 40. In thisembodiment, a semiconductor device can be fabricated similarly to thesemiconductor device of FIG. 6 and FIG. 7, by using the lead frame 40 ofFIG. 9.

[0091] First, the lead frame 40 having the above-mentioned structure isprepared. The lead frame 40 is applied to a mounting process in whichsemiconductor pellets are mounted thereon. A semiconductor pellet 9 a ismounted on each of the heat sinks 5 a and a semiconductor pellet 9 b ismounted on each of the heat sinks 5 b, via adhesive, for example,solder. In this case, the direction of the semiconductor pellets 9 amounted on the heat sinks 5 a and the direction of the semiconductorpellet 9 b mounted on the heat sink 5 b differ from each other by 180degrees.

[0092] Then the lead frame 40 is applied to a wire bonding process.Electrodes not shown in the drawing on each of the semiconductor pellets9 a are electrically coupled with the first electrode portion 7 a andthe second electrode portion 8 a via wires 10 a and 11 a, respectively.Also, electrodes not shown in the drawing on each of the semiconductorpellets 9 b are electrically coupled with the first electrode portion 7b and the second electrode portion 8 b via wires 10 b and 11 b,respectively.

[0093] After finishing the wire bonding process, the lead frame 40 isthen applied to a resin molding process. Major portions on the leadframe 40 are molded by encapsulation resin 22. That is, each groupincluding the first and second electrode portions 7 a and 8 a, thesemiconductor pellet 9 a, and the wires 10 a and 11 a, and each groupincluding the first and second electrode portions 7 b and 8 b, thesemiconductor pellet 9 b, and the wires 10 b and 11 b are respectivelymolded by the encapsulation resin 22.

[0094]FIG. 10 is a schematic partial perspective plan view showing thelead frame 40 after forming the encapsulation resin 22 in each of theabove-mentioned groups. An area encircled by a chain line in FIG. 10corresponds to an area where the encapsulation resin 22 is formed. Also,in FIG. 10, the structure under the encapsulation resin 22 isperspectively shown. The encapsulation resin 22 has recessed portions orconcave portions 23 such that portions of the coupling strips 6 a and 6b near the heat sinks 5 a and 5 b are covered by the encapsulation resin22 and other portions of the coupling strips 6 a and 6 b are exposed.The first band shaped members 2 a and 2 b are exposed.

[0095] Thereafter, the lead frame 40 molded by the encapsulation resin22 is applied to a cutting process. In the cutting process, the leadframe 40 is intermittently transferred, and portions 24 a, 24 b, 25 a,25 b and 26 shown in FIG. 10 by hatching are cut and removedsequentially by using cutting punches and the like, as follows.

[0096] That is, a connecting portion 24 a of the first band shapedmember 2 a located between the heat sinks 5 a and a connecting portion24 b of the first band shaped member 2 b located between the heat sinks5 b are cut by using cutting punches each having approximately V shape,and are removed. Thereby, corner portions of the heat sinks 5 a and 5 bare cut away, and the corner portions are shaped into corners havingobtuse angles. In this case, since the width of each of the connectingportions 24 a and 24 b is relatively small, it is possible to easily cutthese portions.

[0097] Further, a portion 25 a of the second band shaped member 3 abetween the first and second electrode portions 7 a and 8 a which opposeto each other without interposing the coupling strip 6 a therebetween,and a portion 25 b of the second band shaped member 3 b between thefirst and second electrode portions 7 b and 8 b which oppose to eachother without interposing the coupling strip 6 b therebetween are cutand removed.

[0098] Then, a portion 26 which includes exposed portions of thecoupling strips 6 a and 6 b, the bridge portions 20 and portions of thesecond band shaped members 3 a and 3 b connecting to the bridge portions20 are cut and removed.

[0099] Thereby, the first electrode portion 7 a and the second electrodeportion 8 b located at the head of the lead frame 40 are separated fromthe second band shaped members 3 a and 3 b.

[0100] Thereafter, the lead frame 40 is transferred by one pitch byusing the perforations 21. Then, portions which correspond to theconnecting portions 24 a and 24 b and to the portions 25 a and 25 b andwhich are not shown in FIG. 10 by hatching are sequentially orsimultaneously cut and removed. Thereby, the heat sink 5 a and thesecond electrode portion 8 a located at the head of the lead frame 40are separated from the first and second band shaped members 2 a and 3 a,and the heat sink 5 b and the first electrode portion 7 b located at thehead of the lead frame 40 are separated from the first and second bandshaped members 2 b and 3 b. Therefore, two semiconductor devices 50having the semiconductor pellets 9 a and 9 b respectively and having thesame structure are separated.

[0101]FIG. 11 is a perspective view showing the semiconductor device 50fabricated in this way as viewed from the bottom side thereof. Thesemiconductor device 50 has substantially similar structure to that ofthe semiconductor device 30 mentioned above, and has substantially thesame advantageous effects as those of the semiconductor device 30.

[0102] In the lead frame 40 mentioned above, the width of the secondband shaped members 3 a and 3 b can be very small. Also, portions of thesecond band shaped members 3 a and 3 b can be used as portions of thefirst and second electrode portions 7 a, 7 b, 8 a and 8 b. That is,after finishing the cutting process of the lead frame mentioned above,remaining portions of the second band shaped members 3 a and 3 b can beutilized as portions of the first and second electrode portions 7 a, 7b, 8 a and 8 b. Therefore, it is possible to reduce the total width ofthe lead frame 40.

[0103] Also, the space between the half frame structure portions 1 a and1 b can be determined depending on the size or diameter of theperforations 21. Thus, the space between the half frame structureportions 1 a and 1 b can be considerably small. Therefore, it becomespossible to efficiently fabricate a number of semiconductor devices byusing a lead frame having a relatively small size.

[0104] In the above-mentioned lead frames 1 and 40, there are providedtwo electrode portions, that is, the first and second electrodeportions, per one heat sink. Thereby, the semiconductor device 30 and 50each having two electrode portions, that is, the first and secondelectrode portions, can be fabricated. However, in the presentinvention, the number of electrode portions is not limited to that ofthe above-mentioned embodiments. The number of the electrode portionscan be one, three or more, per one heat sink or semiconductor device.

[0105] In the semiconductor device 50, it is possible to provide astepped portion or a slant surface at least at one of opposing endportion of the heat sink and end portions of the first and secondelectrode portions, in a manner similar to the semiconductor device ofFIG. 7 or FIG. 8. Thereby, it is possible to obtain similar effect tothat of the semiconductor device of FIG. 7 or FIG. 8. That is, it ispossible to increase an withstand voltage and to improve moistureresistance.

[0106]FIG. 12 is a cross sectional view showing a schematic structure ofa semiconductor device according to still another embodiment of thepresent invention. FIG. 13 is a perspective view of the semiconductordevice of FIG. 12 from the bottom side thereof.

[0107] In the semiconductor device 51 shown in FIG. 12 and FIG. 13, anend portion of the first electrode portion 7 a and an end portion of thesecond electrode portion 8 a which are opposed to the heat sink 5 a areraised from the exposed surface of the heat sink 5 a. As a resultthereof, the raised end potions of the first electrode portion 7 a andthe second electrode portion 8 a are located inside the encapsulationresin 22. The other structure of the semiconductor device 51 issubstantially the same as the above-mentioned semiconductor device 50,and detailed explanation thereof is omitted here.

[0108] In FIG. 12 and FIG. 13, like reference numerals are used todesignate identical parts to those of the semiconductor device 50. Also,in the description concerning the semiconductor device 51 of FIG. 2 andFIG. 13, it is possible to replace the heat sink 5 a, the firstelectrode portion 7 a, the second electrode portion 8 a, thesemiconductor pellet 9 a and the wires 10 a and 11 a, with the heat sink5 b, the first electrode portion 7 b, the second electrode portion 8 b,the semiconductor pellet 9 b and the wires 10 b and 11 b, respectively.

[0109] The semiconductor device 51 can be fabricated by a methodsubstantially similar to the method of manufacturing the semiconductordevice 50 mentioned above, except that the end portions of the firstelectrode portions 7 a and 7 b and the end portions of the secondelectrode portions 8 a and 8 b are bent or raised from the exposedsurfaces of the heat sinks 5 a and 5 b. Therefore, an explanation of themethod of manufacturing the semiconductor device 51 is omitted here.

[0110] The semiconductor device 51 has the same effects as thosementioned above with respect to the semiconductor devices 30 and 50. Thesemiconductor device 51 further has the following effects.

[0111] In the semiconductor device 51, the end portion of the firstelectrode portion 7 a and the end portion of the second electrodeportion 8 a which are opposed to the heat sink 5 a are raised from theexposed surface of the heat sink 5 a. Therefore, it becomes possible toincrease the distance between the heat sink 5 a and the first electrodeportion 7 a exposed at the bottom surface of the semiconductor device51, and the distance between the heat sink 5 a and the second electrodeportion 8 a exposed at the bottom surface of the semiconductor device51. Therefore, the withstand voltage of the semiconductor device 51 canbe sufficiently large. Also, since the raised end potions of the firstelectrode portion 7 a and the second electrode portion 8 a are locatedinside the encapsulation resin 22, adhesion between the encapsulationresin 22 and the first and second electrode portions 7 a and 8 a isimproved. Thereby, moisture resistance of the semiconductor device isalso improved.

[0112] Further, even when a middle portion of each of the wires 10 a and11 a droops, further fall of each wire is stopped by the raised endportion of each of the first electrode portion 7 a and the secondelectrode portion 8 a. Therefore, it is possible to prevent the wires 10a and 11 a from contacting or approaching a corner edge portion of thesemiconductor pellet 9 a. Thus, it becomes possible to appropriatelyavoid deterioration of an withstand voltage and occurrence of a shortcircuit in the semiconductor device.

[0113] Still further, in the semiconductor device 51, in order toefficiently dissipate heat generated by the semiconductor pellet 9 a, itis possible to make the thickness of the heat sink 5 a larger than thatof each of the first electrode portion 7 a and second electrode portion8 a. In such case, difference between the height of electrodes on thesemiconductor pellet 9 a and the height of wire connecting portions onthe first electrode portion 7 a and the second electrode portion 8 abecomes considerably larger. Therefore, it may be necessary that lengthsof the wires 10 a and 10 b are considerably longer. When the lengths ofthe wires 10 a and 10 b are long, a middle portion of each of the wires10 a and 11 a may easily droop. This may cause contact or approachbetween the wires 10 a and 11 a and a corner edge portion of thesemiconductor pellet 9 a, so that an withstand voltage may bedeteriorated or a short circuit may occur. However, in the semiconductordevice 51, even if a middle portion of each of the wires 10 a and 11 adroops, further fall of each wire is stopped by the raised end portionof each of the first electrode portion 7 a and the second electrodeportion 8 a. Therefore, it is possible to prevent the wires 10 a and 11a from contacting or approaching a corner edge portion of thesemiconductor pellet 9 a. Thus, it becomes possible to appropriatelyavoid deterioration of an withstand voltage and occurrence of a shortcircuit in the semiconductor device. Thereby, in the semiconductordevice 51, it is possible to increase the thickness of the heat sink 5 aand to raise an efficiency of heat dissipation, without causingdeterioration of an withstand voltage and occurrence of a short circuit.

[0114] In the above-mentioned semiconductor devices 30, 50 and 51,electrodes of the semiconductor pellet 9, 9 a and 9 b and the first andsecond electrode portions 7, 7 a, 7 b and 8, 8 a, 8 b are electricallycoupled by using the wires 10, 10 a, 10 b, 11, 11 a and 11 b. However,in place of the wires 10, 10 a, 10 b, 11, 11 a and 11 b, it is possibleto use conductor tapes each having a relatively large width. Especially,it is preferable that, among the electrodes of the semiconductor pellet,an electrode through which a main current flows is electrically coupledwith a corresponding one of the first and second electrode portions viathe conductive tape. Thereby, it is possible to realize a lowon-resistance.

[0115] Generally, when the conductor tapes are used in pace of thewires, there is a possibility that voids are formed in the encapsulationresin and reliability of the semiconductor device is deteriorated. Thisis because, in a resin molding process, the conductor tapes each havinga large width become hindrances to a flow of injected resin material.However, when the lead frame according to the present invention is used,such disadvantage does not occur. The reason for this is as follows.

[0116] That is, in the lead frames 1 and 40, the widths of the couplingstrips 6, 6 a and 6 b are considerably small in the proximity of theheat sinks 5, 5 a and 5 b. Therefore, in the lead frame 1, the spacebetween the coupling strip 6 and the first electrode portion 7 and thespace between the coupling strip 6 and the second electrode portion 8are relatively large. Similarly, in the lead frame 40, the space betweenthe coupling strip 6 a and the first electrode portion 7 a, the spacebetween the coupling strip 6 a and the second electrode portion 8 a, thespace between the coupling strip 6 b and the first electrode portion 7b, and the space between the coupling strip 6 b and the second electrodeportion 8 b are relatively large. Therefore, it is possible to enlarge across sectional area of portions through which the resin can flow, inthe resin molding process. Thereby, it becomes possible to smoothlyinject the resin material into backsides of the conductor tapes. As aresult, it is possible to avoid occurrence of voids in the encapsulationresin and to improve reliability of the semiconductor devices.

[0117] In summary, according to the present invention, it is possible toeasily manufacture a large number of surface mount type semiconductordevices by using a lead frame having a small size. Also, when thesemiconductor device according to the present invention are surfacemounted on a wiring substrate by using solder and the like, it ispossible to precisely mount the semiconductor device on thepredetermined location. Further, according to the present invention, itis possible to realize a semiconductor device having an improvedwithstand voltage and improved moisture resistance.

[0118] In the foregoing specification, the invention has been describedwith reference to specific embodiments. However, one of ordinary skillin the art appreciates that various modifications and changes can bemade without departing from the scope of the present invention as setforth in the claims below. Accordingly, the specification and figuresare to be regarded in an illustrative sense rather than a restrictivesense, and all such modifications are to be included within the scope ofthe present invention. Therefore, it is intended that this inventionencompasses all of the variations and modifications as fall within thescope of the appended claims.

What is claimed is:
 1. A lead frame used for manufacturing semiconductordevices, said lead frame comprising: first and second half framestructure portions; and a plurality of bridge members for connectingsaid first and second half frame structure portions; wherein each ofsaid first and second half frame structure portions comprises: first andsecond band shaped members disposed parallel to each other; a pluralityof island portions for mounting semiconductor pellets thereonrespectively, wherein said plurality of island portions are disposed atpredetermined intervals between said first and second band shapedmembers, and wherein a first end portion of each of said island portionsis connected to said first band shaped member; a coupling strip providedfor each of said island portions, wherein said coupling strip isdisposed between each of said island portions and said second bandshaped member, wherein a first end portion of said coupling strip isconnected to a second end portion of each of said island portions, andwherein a second end portion of said coupling strip is connected to saidsecond band shaped member; and at least one electrode portion which isprovided for each of said island portions and which is to beelectrically coupled with a corresponding electrode of saidsemiconductor pellet mounted on each of said island portions, whereinsaid at least one electrode portion is disposed between each of saidisland portions and said second band shaped member, wherein a first endportion of said at least one electrode portion is connected to saidsecond band shaped member, and wherein a second end portion of said atleast one electrode portion is opposed to said second end portion ofeach of said island portions but is not connected to said second endportion of each of said island portions; and wherein said first andsecond half frame structure portions are disposed symmetrically suchthat said second band shaped members are located inside, and whereinsaid bridge members are connected to said second band shaped member ofsaid first half frame structure portion and to said second band shapedmember of said second half frame structure portion, thereby connectingsaid second band shaped members of said first and second half framestructure portions together.
 2. A lead frame as set forth in claim 1,wherein each of said bridge members has a perforation for transferringsaid lead frame.
 3. A lead frame as set forth in claim 1, wherein, ineach of said half frame structure portions, there are provided twoelectrode portions corresponding to each of said island portions, saidfirst end portions of said two electrode portions are connected to saidsecond band shaped member on both sides of said coupling strip.
 4. Alead frame as set forth in claim 1, wherein each of said bridge membersis located between said coupling strip of said first half framestructure portion and said coupling strip of said second half framestructure portion, wherein a portion of said second band shaped memberof said first half frame structure portion connecting to each of saidbridge members does not overlap a portion of said second band shapedmember of said first half frame structure portion connecting to saidelectrode portion, and wherein a portion of said second band shapedmember of said second half frame structure portion connecting to each ofsaid bridge members does not overlap a portion of said second bandshaped member of said second half frame structure portion connecting tosaid electrode portion.
 5. A lead frame as set forth in claim 1, whereineach of said perforations is located between said coupling strip of saidfirst half frame structure portion and said coupling strip of saidsecond half frame structure portion.
 6. A lead frame as set forth inclaim 1, wherein the width of said coupling strip is smallest at saidfirst end portion and becomes gradually larger toward said second endportion, and wherein the width of said at least one electrode portion islarger than the width of said coupling strip.
 7. A lead frame as setforth in claim 1, wherein the width of said second band shaped member issmaller than the width of said first band shaped member.
 8. A surfacemount type semiconductor device comprising: a conductive island portion;a semiconductor pellet mounted on the top surface of said conductiveisland portion, said semiconductor pellet having at least one electrodeformed on said semiconductor pellet; a conductive strip portion, one endof which connects to a portion of a first end portion of said conductiveisland portion; at least one electrode portion which is electricallycoupled with corresponding one of said at least one electrode of saidsemiconductor pellet, each of said at least one electrode portion doesnot connect to said conductive island portion; and an encapsulationresin which covers and unifies said semiconductor pellet, said electrodeportion, said conductive island portion and said conductive stripportion; wherein, at the bottom surface of said semiconductor device,the bottom surface of said conductive island portion and a portion ofthe bottom surface of each of said at least one electrode portion areexposed from said encapsulation resin; wherein said portion of thebottom surface of each of said at least one electrode portion exposedfrom said encapsulation resin and the bottom surface of said conductiveisland portion are coplanar with each other; wherein, at a side surfaceof said encapsulation resin, a first end portion of each of said atleast one electrode portion and a second end portion of said conductivestrip portion are exposed from said encapsulation resin; wherein thewidth of each of said at least one electrode portion is larger than thewidth of said conductive strip portion; and wherein a seond end portionof each of said at least one electrode portion is raised from saidexposed surface of each of said at least one electrode and is locatedinside said encapsulation resin.
 9. A surface mount type semiconductordevice as set forth in claim 8, wherein said conductive island portionfunctions as a heat sink.
 10. A surface mount type semiconductor deviceas set forth in claim 8, wherein said at least one electrode portioncomprises a plurality of electrode portions.
 11. A surface mount typesemiconductor device as set forth in claim 8, wherein said at least oneelectrode portion comprises two electrode portions.
 12. A surface mounttype semiconductor device as set forth in claim 11, wherein saidencapsulation resin has a concave portion formed in said side surface ofsaid encapsulation resin, a second end portion of said conductive stripportion protrudes from said concave portion, and first end portions ofsaid two electrode portions protrude from both side of said concaveportion in said side surface of said encapsulation resin.
 13. A surfacemount type semiconductor device as set forth in claim 8, wherein said atleast one electrode is electrically coupled with said at least oneelectrode on said semiconductor pellet by wire bonding.
 14. A surfacemount type semiconductor device as set forth in claim 8, wherein, amongsaid at least one electrode on said semiconductor pellet, an electrodethrough which a main current is to flow is electrically coupled with acorresponding one of said at least one electrode portion via aconductive tape.